(1) Dilute U Impurity Systems : Single-site properties of U ions have been investigated in dilute UAI_2 and U_2Zn_<17>, with counterpart dense compounds showing quite contrasting magnetic behavior, by using respectively two different non-magnetc matrices with significantly different lattice parameters. In all the cases, the observed behavior can be explained semi-quantitatively in terms of Kondo effect under crystal field. But differently from Ce-based 4f systems, the behavior of the dense 5f compounds cannot be described as simple collection of the U impurities in the corresponding matrices. Moreover, the variation of the characteristic energy-scale of the system is not at all monotonous against that in the lattice parameters.(2) Systematics of the Spin Dynamics of U Compounds : The antiferromagnetic U_3Pd_<20>Si_6 (T_N=19 K) was previously characterized as a typical localized 5f moment system. In NMR measurements, we have found that the nuclear longitudinal relaxation time T_1 increa
… Moreses almost linearly with T above about 30 K. This indicates that the low-energy spin dynamics can be understood in terms of localized 5f moment also from the NMR viewpoint, but a strongly T-dependent, large relaxation rate of the 5f moment shows that single-site dynamics due to hybridization between 5f and conduction electrons dominate the low-energy spin dynamics in the paramagnetic state. The observed behavior has many similarities to those on U compounds with relatively high ordering temperatures such as UP, UAs and U_3P_4, and are considered as common characteristics in magnetically ordering U systems that are close to the localized moment limit.(3) Multi-Q Magnetic Structure of U Compounds : We have found fine structures in the ^<75>As NMR spectrum at 4.2 K in the magnetically ordered double-Q type IA state. These structures are very likely to be related to the multi-Q structure, and can be an evidence for the quadrupole order in the double-Q state.(3)U化合物の多重Q磁気構造:UAsの秩序状態で^<75>As核NMRスペクトルに多重Q磁気構造に関連すると考えられる微細な構造を見い出した。これは4重極あるいは8重極の秩序を反映している可能性がある。 Less